Leaf Equivalent Water Thickness assessment using reflectance at optimum wavelengths

Abstract

Leaf water content is an important parameter in environmental monitoring. The present study investigated the relation between leaf Equivalent Water Thickness (EWT) as a parameter to estimate the leaf water content and the reflectance in 400-2,500 nm spectral range. The data used were the well-known Leaf Optical Properties Experiment 93 (LOPEX93) field collected data. Four hundred leaf samples were used, 320 of which for modelling and the remaining 80 for testing the model. Four different approaches were investigated in this study: 1) linear regression between reflectance in individual wavelength and EWT; 2) the difference of reflectance in two wavelengths and EWT; 3) ratio of reflectance in two wavelengths and EWT; and finally 4) the normalized difference of reflectance in two different wavelengths and EWT. The results showed that the band combinations such as ratio and normalized difference had higher regressions with leaf water content. In addition, the findings of this study showed that some parts of the near infrared (NIR) and short wave infrared (SWIR) of the spectrum provided higher accuracies in EWT assessment, and correlations of more than 90% were achieved. Finally, this investigation showed that a wide range of wavelengths could be used for EWT assessment task. Despite the general belief in using water absorption bands for leaf water content assessment, this study shows that water absorption bands are not necessarily productive as other wavelengths have the potential to generate better results.

Using Remote Sensing to Identify Drivers behind Spatial Patterns in the Bio-physical Properties of a Saltmarsh Pioneer

“…The average water content per leaf area was calculated from the photographed and dried leaf samples. The equivalent water thickness (Cw) is then calculated using the corresponding formula ((FW-FD)/Area, see References [54,55]). Average leaf equivalent water thickness (Cw) was found to be 0.0198 ± 0.0043 cm (n = 50).…”

Resposta hiperespectral na determinação do conteúdo de água na folha em diferentes espécies de <i>Eucalyptus</i> spp.

“…A densidade equivalente da água (do inglês equivalent water thickness-EEA) é outro parâmetro muito utilizado para quantificar água na folha, porém este estima a proporção de água por área foliar (YI et al, 2012;MOBASHERI;FATEMI, 2013; e varia de acordo com as características das folhas (CECCATO et al, 2001). …”

“…O CRA é uma variável dada em porcentagem (%) que quantifica a proporção de água e matéria seca na vegetação (FERNANDES et al, 2015;ARDNT et al, 2015), enquanto que o EEA estima a quantidade de água pela área foliar (YI et al, 2013;MOBASHERI;FATEMI, 2013; e varia de acordo com as características das folhas (CECCATO et al, 2001).…”

Dados hiperespectrais na determinação do conteúdo relativo de água na folha em cana-de-açúcar

“…Atualmente, e desde há décadas, o sensoriamento remoto tem-se tornado uma ferramenta auxiliar na determinação de parâmetros bióticos e abióticos da vegetação, sendo um deles o estado hídrico (BEHMANN; STEINRÜCKEN; PLÜMER, 2014; ECARNOT; COMPAN; ROUMET, 2013;MOBASHERI;FATEMI, 2013;PACUMBABA;BEYL, 2011;SANCHES et al, 2013).…”

“…The EWT parameter proved to be sensitive faster to changes in the water content in the leaf which allowed suggest that further studies should consider the EWT to estimate the water status of sugarcane leaves. ;FATEMI, 2013;ULLAH et al, 2014;YEBRA et al, 2013;YI et al, 2013;ZHANG et al, 2012). Outros estudos utilizam conteúdo relativo de água (CRA) (CECCATO et al, 2001;DAVIDSON;WILMSHURST, 2006;ZYGIELBAUM et al, 2009).…”